본 논문은 MR댐퍼를 기반으로 하는 제어시스템을 대형 구조물 등에 설치할 수 있도록 간편한 알고리즘을 구현하였다. 아울러, MR댐퍼를 기반으로 하는 스마트 수동제어 시스템을 제안하였다. MR댐퍼는 최근에 각광 받는 반능동 제어 장치로써, 배터리와 같은 소규모 전력을 사용하고, 이에 따른 비상시의 신뢰성, 그리고 상...

u(t) c 1 2 k 3 m f c Abstract A preliminary study was conducted to investigate numerical models that can be used to simulate the dynamic behaviour of a damper based on magnetorheological (MR) materials. Several articles presenting the results of experimental testing and mathematical modelling have been published recently. The goal for this study was to implement a selected model into the finite element method (FEM) for structural dynamic analysis purposes in the time domain. A simplified controllable spring-dashpot-friction element was implemented as a user element subroutine ("smart connector element") into the ABAQUS/Standard FEM-program. The model was verified by numerical comparisons. It was observed that the smart connector element can be applied to simulate a similar dynamic response to that measured in the experiments. Therefore, it can be employed to analyze adaptive structures in which the MR-damper is utilized to control dynamic properties. Preface This paper presents available models for magnetorheological (MR) materials and dampers that can be applied in structural analysis. The work was carried out in VTT´s technology theme: Intelligent Products and Systems under the topic Embedded Structural Intelligence. The objective in this topic is to cost-efficiently embed intelligence into structures, which can enable utilisation of entirely new types of product concepts with high performance and reliable operation. The key focus area is to develop functional materials, affordable wireless measurement technology and control, which are adaptable to operating conditions, and to apply these in vibration, durability and shape control.

t years, considerable attention has been paid to research elopment of structural control devices, with particular emon alleviation of wind and seismic response of buildings ges. In both areas, serious efforts have been undertaken in two decades to develop the structural control concept into ble technology. Full-scale implementation of active conems have been accomplished in several structures, mainly n; however, cost effectiveness and reliability considerave limited their wide spread acceptance. Because of their ical simplicity, low power requirements, and large, conforce capacity, semiactive systems provide an attractive ive to active and hybrid control systems for structural vireduction. In this paper we review the recent and rapid ments in semiactive structural control and its implemenfull-scale structures.

steel frame eq uipped with MR -dampers on the 1 st , 3 rd and 5 th floors. In experimental test s, an EL Centro earthquake, a Kobe earthquake and a Chi -Chi earthquake (station TCU067) are used as ground excitation s. Various control algorithms are used for this semi -active control studies , including the Decentralized S liding Mode Control (DSMC) , LQR control and passive -on and passive -off control. Each algorithm is formulated specifically for the use of MR -damper s. The performance of each algorithm is evaluated based on the results of shaking table test s, and the advantages of each a lgorithm is compared and discussed. The reduction of the story drift and acceleration throughout the structure is examined.

With the development of the control research, intelligent control has become one of the most popular research topics worldwide. The traditional method of Numerical simulation on control theories are realized by the programs in MATLAB, which is based on numbers of assumptions and simplification. However, it is difficult to ensure that the seismic response of the structure is always in linear elastic state during the process of hazard evolution under strong earthquake so that certain errors during such simulation are inevitable. In order to solve this problem, a numerical method of the realization of semi-active control in commercial finite element software ABAQUS is proposed in this paper. One of the main advantages of this method is that the structural plastic response can be taken into account. In this paper, the seismic response of a bridge with three-span continuous girder is numerically studied, and the semi-active control is successfully realized in ABAQUS. The proposed method can be used to carry out the refined simulation of the seismic response of the structures with semi-active control set. The highlight of this paper is to provide an effective approach for the research of intelligent control.

Whole body vibration in operational vehicles can cause serious musculo-skeletal disorders among the exposed workers. Consequently, considerable efforts have been made to protect vehicle operators from potentially harmful vibration. This thesis was aimed at the development of a semi-active suspension seat equipped with a magneto-rheological (MR) fluid damper. A damper controller was synthesized to minimize the vibration transmitted to the seated body and the frequency of end-stop impacts, which is known to induce high intensity vibration or shock motions to the seated occupant. A suspension seat was modeled by considering the kinematic non-linearity due to the cross-linkages and the damper link, while the cushion characteristics were linearized about the operating preload. The force-velocity properties of the MR damper were modeled by piecewise polynomial functions of applied current on the basis of the laboratory-measured data. The kineto-dynamic model of the suspension seat was thoroughly validated using the laboratory-measured responses under harmonic excitations in the 0.5 to 10Hz range. The performance characteristics of the passive suspension seat model were evaluated under different vehicular excitations in terms of frequency-weighted rms acceleration, vibration dose value (VDV), seat effective amplitude transmissibility (SEAT) and VDV ratio. These performance characteristics are also evaluated under amplified vehicular excitations in order to investigate the frequency as well as the potential suppression of end-stop impacts. The controller synthesis was realized in two stages: (1) attenuation of continuous vibration; and (2) suppression of end-stop impacts. Two different algorithms were explored in the first stage synthesis, which included a sky-hook control algorithm and a relative states feedback control algorithm. Each algorithm was further utilized in two different control current modulations. The performance potentials of each control synthesis were investigated using the 2 MATLAB Simulink platform under harmonic, transient, and random vehicular excitations in terms of SEAT and VDV ratio. One controller design (overall best suited for implementations) was subsequently implemented in a hardware-in-the-loop (HIL) test platform coupled with a MR-fluid damper mounted on an electro-hydraulic actuator that was linked to the HIL simulation platform. The semi-active suspension seat performance characteristics were further evaluated under different excitations using the selected control scheme. The results showed that the selected control scheme yielded SEAT and VDV ratio reductions in the 5 to 30% range depending upon the nature of excitations. The implementation of the second-stage controller, which was tested only by simulations, entirely eliminated the occurrence of end-stop impacts at nominal vibration level and attenuated the end-stop impact severity of three times amplified excitations by up to 10% . The results further suggested that the use of MR-fluid damper in suspension seat was most beneficial to city buses and class I earth moving vehicles amongst the selected inputs.

We propose a new active vibration control strategy of structural systems based on the information of future seismic waveform observed in remote observation sites. The observed waveform information of the remote site is transmitted by a waveform transmission network to the structure under control. The waveform transmission network is realized by interconnecting multiple controlled structures and observation sites. By using the remote waveform containing the future information of the disturbance at the location of the controlled structure, we propose an active control method that achieves fairly higher control performance over conventional methodologies. A preview control consisting of the state-feedback and feedforward control (preview action) is adopted as the control law. For the preview action, a future seismic waveform in some time interval is needed. Because the future seismic waveform is not available, the preview action contributing the performance improvement is generally impossible. To get over this difficulty, an artificial intelligence–based waveform estimation system to estimate the future seismic waveform is proposed. The core of the wave estimation system is a multi-layered artificial neural network. Through a small-scale simulation study with a recorded seismic event in Japan, we show that the proposed control method achieves much higher control performance over the optimized H 2 state-feedback control law.

Vehicle manufacturers have been attempting to increase engine efficiency and decrease pollution through various methods. Variable valve actuation technology is one of these methods. Several mechanisms have been established already and have been used to develop this technology. However, these systems have common problems such as complex design, large volume, low response rate, and high-energy consumption. In this study, a novel variable valve actuation device that is compact and requires less energy was developed using magnetorheological (MR) fluid technology. The main components used in this device are an MR valve, passive buffer spring, cam, and rocker arm. This study was divided into three parts. First, an MR valve train was designed. This valve train can be constructed easily, and has fewer hydraulic and mechanical components and consumes less energy than other technologies. Second, the magnetic plate block design was optimized to obtain the required control force at optimal volume and energy. Finally, dynamical simulations pertaining to the springs and the structure were executed to analyze the dynamic condition of the valve. The simulation results indicated that the proposed MR valve could effectively provide functions of variable valve timing and variable valve lift by dynamically controlling the external current in the magnetic coil.

Under high velocity, pulse type near source earthquakes semi-active control systems are very effective in reducing seismic response base isolated structures. Semi-active control systems can be classified as: 1) independently variable stiffness, 2) independently variable damping, and 3) combined variable stiffness and damping systems. Several researchers have studied the effectiveness of independently varying damping systems for seismic response reduction of base isolated structures. In this study effectiveness of a combined system consisting of a semi-active independently variable stiffness (SAIVS) device and a magnetorheological (MR) damper in reducing seismic response of base isolated structures is analytically investigated. The SAIVS device can vary the stiffness, and hence the period, of the isolation system; whereas, the MR damper enhances the energy dissipation characteristics of the isolation system. Two separate control algorithms, i.e., a nonlinear tangential stiffness moving average control algorithm for smooth switching of the SAIVS device and a Lyapunov based control algorithm for damping variation of MR damper, are developed. Single and multi degree of freedom systems consisting of sliding base isolation system and both the SAIVS device and MR damper are considered. Results are presented in the form of nonlinear response spectra, and effectiveness of combined variable stiffness and variable damping system in reducing seismic response of sliding base isolated structures is evaluated. It is shown that the combined variable stiffness and variable damping system leads to significant response reduction over cases with variable stiffness or variable damping systems acting independently, over a broad period range.

Under extreme service conditions in vehicle suspension systems, some defects exist in the hardening, bodying, and poor temperature stability of magnetorheological (MR) fluid. These defects can cause weak and even invalid performance in the MR fluid damper (MR damper for short). To ensure the effective validity of the practical applicability of the MR damper, one must implement an online state-monitoring sensor to monitor several performance factors, such as acceleration. In this empirical work, we propose a new energy-harvesting device system for the wireless sensor system of an MR damper. The monitoring sensor system consists of several components, such as an energy-harvesting device, energy-management circuit, and wireless sensor node. The electrical energy harvested from the kinetic energy of the MR fluid that flows within the MR damper can be automatically charged and discharged with the help of an energy-management circuit for the wireless sensor node. After verifying good performance from each component, an experimental apparatus is built to evaluate the feasibility of the proposed self-powered wireless sensor system. The measured results of pressure, temperature, and acceleration data within the MR damper clearly demonstrate the practical applicability of monitoring the operating work states of the MR damper when it is subjected to sinusoidal excitation.

Two semiactive control schemes for protecting structures against earthquakes using magnetorheological dampers as control devices are presented. The design of the schemes is based on the LuGre's dynamic friction model adapted to describe the behavior of dampers. Seismic attenuation with respect to the case of noncontrolled structures is demonstrated. Numerical simulation of a scaled structure under seismic excitation show very good performance.

Traditional structure was used as an active control mechanism and structure system under the stable situation in the time history of dynamic response. In order to attain the energy dissipation, the additional applied work depends on the deformation of control elements. The new control mechanism, Neutral Equilibrium System (NES), will be introduced in this paper. NES is composed of unstable control mechanism and stable structure frame. It has advantages of all functions; a merit of active control method and it does not require the extra energy supply. The earthquake record or the histories of harmonic loading are used as input data to discuss the results of numerical simulation in investigating the stability, usability and effect of this control mechanism. The results indicate that this mechanism should be controlled thoroughly. Under appropriate control law, the control state is nearly perfect. Nevertheless, the external energy is required for control system to operate by using the control law of related displacement. Thus, NES should match with the control law of related velocity. The entire capability of active control can be performed under the condition of direct velocity and control feedback control method when no power energy is supplied.

To survive in nature, animals adjust the characteristics of their legs or fins to adapt the motion to their environment. Inspired by the locomotion of animals, a study on the tunable stiffness and damping of a leg will help in the development of intelligent locomotion robots. In this paper we report on the development and experiment of a novel and simple robotic leg that can be adapted to the environment via a smart magnetorheological fluid (MRF). The robotic leg consists of a rotation MRF damper, a torsional spring, a 'foot' and a 'leg'. The curved part of the 'foot' makes contact with the grounds while the other end is linked to an outer cylinder of the MRF damper with an inelastic cable. The variable force arm rising from the MRF damper and the torsional spring can help the leg adapt to a changing environment. The characteristics of the MRF damper have been investigated and a model is built to describe its mechanical features when different currents are applied to the MRF damper. A test on a linear dynamic test instrument has been conducted to verify the accuracy of the model. The robotic leg is installed in a locomotion platform to investigate the speed of its locomotion and the cost of the transport; the result demonstrated the feasibility and adaptability of the leg when walking on hard terrain. Its simple structure, high adaptability, and easy control of the MRF leg helped in the design and development of a high performance field robot that can adapt to various environments.

Title of dissertation: SYMBOLIC AND NUMERIC SOLUTIONS OF MODIFIED BANG-BANG CONTROL STRATEGIES FOR PERFORMANCE-BASED ASSESSMENT OF BASE-ISOLATED STRUCTURES Robert R. Sebastianelli, Jr., Doctor of Philosophy, 2005 Dissertation directed by: Associate Professor Mark A. Austin Department of Civil and Environmental Engineering and Institute for Systems Research This work explores symbolic and numeric solutions to the Lyapunov matrix equation as it applies to performance-based assessment of base-isolated structures supplemented by modified bang-bang control. Traditional studies of this type rely on numeric simulations alone. This study is the first to use symbolic analysis as a means of identifying key “cause and effect” relationships existing between parameters of the active control problem and the underlying differential equations of motion. We show that symbolic representations are very lengthy, even for structures having a small number of degrees of freedom. However, under certain simplifying assumptions, symbolic solutions to the Lyapunov matrix equation assume a greatly simplified form (thereby avoiding the need for computational solutions). Regarding the behavior of the bang-bang control strategy, further analysis shows: (1) for a 1-DOF system, the actuator force acts very nearly in phase, but in opposite direction to the velocity (90◦ out of phase and in opposite direction to the displacement), and (2) for a wide range of 2-DOF nonlinear base-isolated models, bang-bang control is insensitive to nonlinear deformations in the isolator devices. Through nonlinear time-history analysis, we see that oneand two-DOF models are good indicators of behavior in higher DOF models. An analytical framework for system assessment through energyand powerbalance analysis is formulated. Computational experiments on base-isolated systems are conducted to identify and quantitatively evaluate situations when constant stiffness bang-bang control can significantly enhance overall performance, compared to base isolation alone, and assess the ability of present-day actuator technologies to deliver actuator power requirements estimated through simulation. SYMBOLIC AND NUMERIC SOLUTIONS OF MODIFIED BANG-BANG CONTROL STRATEGIES FOR PERFORMANCE-BASED ASSESSMENT OF BASE-ISOLATED STRUCTURES by Robert R. Sebastianelli, Jr. Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2005 Advisory Committee: Associate Professor Mark A. Austin, Chair/Advisor Associate Professor Raymond Adomaitis Professor Emeritus Pedro Albrecht Professor Bilal M. Ayyub Assistant Professor Ricardo A. Medina c © Copyright by Robert R. Sebastianelli, Jr. 2005 This dissertation is dedicated to my wife, Mary. For her love, taste, judgment, and style.

Title of Thesis: THE EFFECTS OF UNMITIGATED IDLE TIME ON THE PERFORMANCE OF MAGNETORHEOLOGICAL DAMPERS AS A STRUCTURAL PROTECTIVE SYSTEM. Sami Ur-Rahman Khan Master of Science Civil and Environmental Engineering 2018 Thesis Directed By: Dr. Brian Phillips, Assistant Professor. Civil and Environmental Engineering This thesis discusses the long-term performance degradation of seismic protective systems due to age and inactivity (termed “idle time effects”). Over the lifetime of a structures there is the potential for a significant reduction in ability for the structural control systems to mitigate earthquakes. This can affect the resilience of the structure and lead to uncertainty in engineering judgement when designing seismic protective systems. Further research into these idle time effects could help to create solutions to mitigate age-dependent performance loss. This paper will use magneto-rheological (MR) dampers, which serve as a good analog for other semi-active control devices, to study idle time effects on seismic protection. MR dampers provide controllable damping through the magnetization of small MR particles in a carrier fluid. These particles can settle over time, influencing their performance. Using a model MR fluid, accelerated testing was performed to analyze the consequences of idle time. THE EFFECTS OF UNMITIGATED IDLE TIME ON THE PERFORMANCE OF MAGNETORHEOLOGICAL DAMPERS AS A STRUCTURAL PROTECTIVE SYSTEM.

Three semi-active control methods are investigated for use in a suspension system using a commercial magnetorheological damper. The three control methods are the limited relative displacement method, the modified skyhook method, and the modified Rakheja-Sankar method. The method of averaging has been adopted to provide an analytical platform for analyzing the performance of the different control methods. The analytical results are verified using numerical simulation, and further are used to assess the efficiency of different control methods. An experimental test bed has been developed to examine the three control methods under sinusoidal and random excitations. Both analytical and experimental results confirm that the Rakheja-Sankar control and modified skyhook control methods significantly reduce the root-mean-square response of both the acceleration and relative displacement of the sprung mass, while the limited relative displacement controller can only control the relative displacement of the suspension system.

This work investigates the efficiency of mixed base isolation, combining passive isolation bearings with semi-active (SAC) devices, to reduce the floor spectral acceleration in the vicinity of the non-isolated modes’ frequencies. Both analytical and experimental studies have been carried out. Analytical results of the behaviour of a multiple degree of freedom base isolated structure demonstrate the efficacy of the method. Though the considered controller is based on a reduced order model with only two degrees of freedom (2 DOF) without spillover compensation, the results show that, for the type of structures studied here, spillover effects are not considerable. An experimental study of a 2 DOF model of a base isolated structure equipped with a semi-active magneto-rheological (MR) damper has been carried out. Due to limitations of the experimental set-up, it has not been possible to obtain direct experimental evidence of the efficacy of SAC control to improve floor spectra. Nevertheless, based on the good agreement between analytical and experimental results which validate the considered MR model and control algorithm, numerical analyses of more relevant configurations illustrated the benefit of the utilization of such devices.

This work describes a new technique for parameter estimation for magnetorheological dampers which relies on rearrangement of the constitutive equations for the modified Bouc–Wen model to obtain a cost function using only predetermined time series values. Advantages of the new method include reliable convergence under low-noise conditions with only broad constraints and single-stage estimation of seven damper parameters.

This thesis explores semi-active structural control methods for mitigating damage during seismic events. Semi-active devices offer the adaptability of active devices in conjunction with low power requirements and thus the reliability of passive devices. A number of structural applications utilising semi-active resetable devices in structural control are described and analysed. A distinguishing feature of this research is the novel design of a large-scale resetable device developed, manufactured and extensively tested. This design dramatically extends the capabilities of resetable devices by readily manipulating the device response to the structural demands and specific structural control requirements. In particular, the unique ability to use these devices to reshape or sculpt structural hysteretic behaviour offers significant new opportunities in semi-active structural control. The results indicate improvements in structural performance during seismic events is gained by approaches to structural control and enhanced damping methods that challenge conventional methods. Using an array of performance metrics the overall structural performance is examined without the typically narrow focus found in other studies. Suites of earthquake ground motion records are utilised to avoid bias to any particular type of motion and statistical analysis of the performance over these suites indicates the overall efficacy of the resetable devices in each case considered. A model that accurately captures all the device dynamics is developed, which can be used for a variety of device types and designs. In addition, the testing capabilities of structural control methods is enhanced by the development of a high speed, real-time hybrid test procedure providing a link between pure simulation and full-scale testing to increase confidence before investing in large experiments. Finally, the resetable devices are extended to improve the response force to size ratio, which additionally increases the force-displacement manipulation ability.

This thesis considers two main issues concerning the application of a rotary type magnetorheological (MR) damper for damping of flexible structures. The first is the modelling and identification of the damper property, while the second is the formulation of effective control strategies. The MR damper is identified by both the standard parametric Bouc-Wen model and the non-parametric neural network model from an experimental data set generated by dynamic tests of the MR damper mounted in a hydraulic testing machine. The forward model represents the direct dynamics of the MR damper where velocity and current are used as input and the force as output. The inverse model represents the inverse dynamics of the MR damper where the absolute velocity and absolute force are used as input and the damper current as output. For the inverse model the current output of the network must always be positive, and it is found that the modelling error of the inverse model is significantly reduced when the corresponding input is given in terms of the absolute values of velocity and damper force. This is a new contribution to the inverse modelling techniques for the control of MR dampers. Another new contribution to the modelling of an MR damper is the use of experimental measurement data of a rotary MR damper that requires appropriate filtering. The semi-systematic optimisation procedure proposed in the thesis derives an effective neural network structure, where only velocity and damper force are essential input parameters for the MR damper modelling. Thus, for proper training, the quality of the velocity data is very important. However, direct velocity measurement is not easy. From the displacement data or the acceleration data, velocity can be determined by using simple differentiation or integration, respectively, but these processes add undesirable noise to the velocity. Instead the Kinematic Kalman Filter (KKF) is an effective means for estimation of velocity. The KKF does not directly depend on the system or structural model, as it is the case for the conventional Kalman filter. The KKF fuses the displacement and the acceleration data to get an accurate and robust estimate of the velocity. The simplicity of the network and the application of velocity in terms of KKF is a novel contribution of the thesis to the generation of a training set for neural network modelling of MR dampers. The development of the control strategies for the MR damper focuses on the introduction of apparent negative stiffness, which basically leads to an increased local motion of the damper and thereby to increased energy dissipation and damping. Optimal viscous damping (VD) is chosen as the benchmark control strategy, used as reference case for assessment of the proposed control methods with negative stiffness. Viscous damping with negative stiffness (VDNS) initially illustrates the effectiveness of the negative stiffness component in structural damping. In a linear control setting negative stiffness requires active control forces, which are not realizable by the purely dissipative MR damper. Thus, these active components are simply clipped in the final control implementation. Since MR dampers behave almost as a friction damper improved damping performance can be obtained by a suitable combination of pure friction and negative damper stiffness. This is realized by amplitude dependent friction damping with negative stiffness (FDNS), where the force level of the friction component is adaptively changed to secure the optimal balance between friction energy dissipation and apparent negative stiffness. This type of control model for semi-active dampers is rate-independent and conveniently described in terms of the desired shape of the associated hysteresis loop or force-displacement trajectory. The final method considered for control of the rotary MR damper is a model reference neural network controller (MRNNC). This novel control approach is designed and trained based on a desired reference damper model, which in this case is the amplitude dependent friction damping with negative stiffness (FDNS). The idea is to train the neural network of the controller by data derived explicitly from the desired shape of the force-displacement loop at pure harmonic motion. In this idealized representation the optimal relations between friction force level, negative stiffness and response amplitude can often be given explicitly by e.g. maximizing the damping ratio of the targeted vibration mode. Consequently the idea behind this trained neural network is that the optimal properties of the desired hysteresis loop formulation can be extrapolated to more general and non-harmonic response patterns, e.g. narrow-band stochastic response due to wind, wave, traffic or even earthquake excitation. Numerical and experimental simulations have been conducted to examine the performance of the proposed control strategies. Force tracking by using an inverse neural network of the MR damper is improved by a low-pass filter to reduce the noise in the desired current and a simple switch that truncates negative values of the desired current. The performance of the collocated control schemes for the rotary type semi-active MR damper are initially verified by closed loop dynamic experiments conducted on a 5-storey shear frame structure exposed to harmonic base excitation. The MR damper is mounted on the structure so that it operates on the relative motion between the ground base and the first floor of the shear frame. The shear frame structural model is initially experimentally identified, where mass and stiffness of the model is determined by an inverse modal analysis based on the natural frequencies obtained experimentally. The damping matrix is subsequently determined from the estimated damping ratio obtained by free decay tests. The results in the thesis demonstrate that introducing apparent negative stiffness to the control of the MR damper significantly decreases both the top floor displacement and acceleration amplitudes of the shear frame structure. The structural damping ratios obtained from the response curves of the experiments correspond well to the expected values. This indicates that the mean stiffness and mean energy dissipation of the control forces are predicted fairly accurate. A final numerical investigation is based on a classic benchmark problem for earthquake protection of a multi storey building. The seismic response of the base-isolated benchmark building with an MR damper installed between the ground and the base is illustrated, and the effectiveness of negative stiffness of the control strategies is verified numerically. Similarly, the response of another wind excited benchmark building installed with MR dampers is demonstrated and the performance shows satisfactory result. The main contributions to this thesis are the novel modelling approach to the direct and the inverse dynamics of a rotary MR damper from experimental data, the development of model based semi-active control strategies for the MR damper, the effective introduction of negative stiffness in the control of semi-active dampers and the demonstration of effectiveness and closed loop implementation of the control techniques on both a shear frame structure and a numerical benchmark problem.